In communication process between information processing apparatuses via communication relay apparatuses such as NAT routers, proxy servers, and the like, if they do not communicate with each other for a predetermined period of time, a communication relay apparatus may cut off connection. In view of this, the communication relay apparatuses communicate with each other to maintain connection at a constant time interval (Keep Alive, HeartBeat communication). For example, the following Patent Document 1 describes Keep Alive.
Patent Document 1: Japanese Patent Application Laid-open No. 2009-232358